TAMPA, Fla. 
Encircled by fellow volunteers for Barack Obama, Katie Sprung scanned a clipboard full of addresses. "We don't all three go to the same house, right?" asked Sprung, one of the president's neighborhood team leaders. No, she was told - just one volunteer per door. As they departed, another staff member said into the telephone: "We're not targeting independents anymore. We're focusing on our supporters."

Across Old Tampa Bay, Terry and Barbara Bear sat in a Mitt Romney field office. Sitting under photos of Ronald Reagan, the St. Petersburg, Fla., couple staffed phones programmed to dial households across the largest of all swing states. "I'm getting a lot of wrong numbers today," Terry Bear replied before reaching a live Republican voter, whom he asked to vote early. "Well, thank you for your support, ma'am," he said. "It's time for a change in this country."

Sprung and the Bears, and thousands of volunteers like them around the country, help anchor what politicos call the "ground game" or "GOTV" - get out the vote - that turns months of work into actual votes. For all the campaigns' sophisticated marketing research, hundreds of millions of dollars of advertising and the emphasis on nationally televised debates, the outcome could rest on these volunteer surrogates and their outreach.

"We believe that above all of the other action, that personal contact is what is so important in making people feel a connection, like they are part of something bigger in the country," said Ron Brown, a retired engineer and Obama neighborhood team leader in Seminole, Fla.

That sentiment, it's safe to say, goes right to the top. "This will probably be a turnout election, where people working hard, bringing folks into the polls who might otherwise say, `Oh it's just one vote,'" Romney told an overflow crowd in Wisconsin on Friday. "Let me tell you, one vote times a hundred thousand is a hundred thousand."

The ground-game effort mixes two equally pivotal disciplines - the science of analyzing data to identify likely or potential supporters and the art of personal contact, all the while trying not to alienate battleground residents who, frankly, sometimes get tired of all the attention.

"Well, the way to not get any more calls is to tell us you've voted," Terry Bear told one man who answered the phone.

Four years ago, Obama's organization ran circles around John McCain's. In 2004, it was the Republican infrastructure that won out, helping President George W. Bush to a close but decisive re-election. Those two successes are precisely what the campaigns are trying to replicate, says Brett Doster, a Tallahassee GOP strategist for Romney's Florida campaign.

Each camp has put a lot of energy into registering new voters and is pushing early voting in states that allow it. The latter approach is, for Republicans, a newer emphasis. In Florida, they've largely succeeded in cutting into the early leads that Obama amassed in 2008. Republicans say that's evidence of momentum that will carry though to Election Day. Democrats counter that the GOP is simply moving reliable votes from the Election Day tally to the early voting totals.

Besides the usual door-knocking and phone calls and other now-expected techniques - the deployment of political and entertainment celebrities and the use of social media, which dwarfs the 2008 campaign - the campaigns use creative, even quirky tactics. They also cultivate nuances from state to state as they tailor messages to turnout efforts.

In Ohio, Obama trumpets the auto bailouts around cities with car plants and suppliers. In Colorado, the Romney team is trying to drive up rural turnout, not usually a focus in that state's campaigns. In Florida, Romney has dispatched former Gov. Jeb Bush and Sen. Marco Rubio to talk with small groups of non-Cuban Hispanics in central Florida. Democrats here are trying to make inroads with younger Cubans, whose parents and grandparents are hard-line, anti-Castro Republicans. They also want to peel off older Republicans who might go with Obama because of Medicare and Social Security.

Romney's top pollster, Neil Newhouse, said this week that independents will make the difference. That squares with the assignment handed to Romney volunteer Sarah Partin. As early voting began, the University of South Florida-St. Petersburg senior was in Tierra Verde, an upper middle class, GOP-leaning enclave of Pinellas County, to knock on the doors of undeclared voters.

"It's my job to figure out whether we can count on them," she said. "Mostly, I explain personally what makes me support Romney. We just have to be as nice as possible."

In most states, the Obama camp refuses to disclose little more than the number of field offices. For the record, Obama has 106 in Florida to Romney's 49; in most battlegrounds, Obama's 2008 offices never closed.

Top Obama strategist David Plouffe said in his memoir of the 2008 election that Obama's path to victory was expanding the electorate using person-to-person outreach that began long before typical "get-out-the-vote" efforts. His paid staffers this year point to the job titles of people like Sprung and Brown as the key distinction from Romney's organization.

"When I knock on doors, I'm in my own neighborhood," Sprung said. "I hear their stories, their concerns. I answer questions." Noting that her son is a diabetic who cannot be denied insurance under Obama's Affordable Care Act, she added: "I tell them my story, and why I'm with the president."

However large the operation, it's an inexact exercise, beyond just the inaccurate numbers on phone lists. Witness Sue Smith, a registered Republican in Pinellas County, Fla., who says she is an undecided but regular voter: "I haven't heard from either campaign."

Tampa resident Anthony Arenas said he's a registered Democrat who fielded multiple calls and visits from the Obama campaign. At an early voting site, he emerged from his car and yelled: "Is this where I vote for Mitt Romney?"